High pressure mercury vapor discharge lamp

ABSTRACT

The addition of suitable proportions of mercury iodide and other selected metals to a mercury vapor lamp containing sodium iodide limits the change in operating voltage with time and provides longer life.

United States Patent 1 Divoix et al.

1 1 June 19, 1973' HIGH PRESSURE MERCURY VAPOR DISCHARGE LAMP Inventors:Jacques Climeut Divoix,

Mesnil-le-Roi; Andre Marc V. Taxil, Rueil-Malmaison, both of FranceAssignee: Claude, Paris, France Filed: Aug. 24, 1971 Appl. No.: 174,535

Foreign Application Priority Data Aug. 27, 1970 France 7031287 US. Cl.313/229, 313 225 H0lj 61/20 Field of Search 313/229 Primary ExaminerRoyLake Assistant Examiner-Darwin R. Hostetter Attorney-C. Cornell Remsen,Jr.', Walter J. Baum and Menotti J. Lombardi et al.

[57] ABSTRACT The addition of suitable proportions of mercury iodide andother selected metals to a mercury vapor lamp containing sodium iodidelimits the change in operating voltage with time and provides longerlife.

2 Claims, No Drawings 1 HIGH PRESSURE MERCURY VAPOR DISCHARGE LAMPBACKGROUND OF THE INVENTION The metal halogenides introduced intohigh-pressure mercury-vapor lamps are generally iodides and the metalhalogenide which is added in the present invention is cesium iodide,cesium having a low ionization 1. Field of the Invention 5 energy. Thepresent invention relates to improvements in high-pressure mercury-vaporelectric discharge lamps and, more particularly, to lamps of this typewhich contain, in addition to mercury, alkali metal halogenides.DESCRIPEFERRED 2. Description of the Prior Art In these lamps, luminousradiation is generally produced either by very concentrated intenseemission The following Table 1 shows three examples A, B and rays, as inthe case of metals such as thallium, sodium C of fillings forhigh-pressure mercury-vapor lamps and indium, or by very numerous raysspread over the having a power of 400 watts obtained with an innerentire spectrum as in the case of rare-earth elements or tube having adiameter of 18 mm and a spacing betransition metals such as scandium,hafnium, thorium. tween electrodes of 50 mm. In each example, the left-The lamp is generally formed of an outer glass envelope side columnshows the possible pressure and weight and an inner high pressuredischarge tube of vitreous limits in torrs (millimeters of mercury) andin millimaterial Such as q grams, respectively, of the filling materialsand the The metals are usually introduced into the lamp in 20 right-sidecolumn the values used in an embodiment. the form of halogenides more pr icul rly, in the The left hand column lists the various materials inthe form of iodides which are highly volatile halogenides. compositions.H V One of the most used iodides is sodium iodide which, I he exam leArelates to addition of yttrium and cedue to its low vapor pressure atthe lamp operation sium iodide with mercury iodide in a high-pressuretemperature, is gaseous within the discharge region of mercury-vaporlamp already containing iodides of sothe inner tube and liquid about thetube walls. Due to dium (having a characteristic yellow color), ofthallium a diffusion phenomenon through the tube walls, the So- (havinga green color) and of indium (having a blue dium iodide is decomposedand the sodium leaves the color). inner area resulting in an enrichmentof iodine inside The example B relates to addition of yttrium and cethetube, which restrains the electric discharge phei m iodide with mercuryiodide in a high-pressure nomenon causing an increased voltage acrosselectrode mercury-vapor lamp already containing sodium Iodid terminalsafter a few hundreds of Operation h r and scandium, which have a veryclose color spectrum. renders lighting difficult. In the example C,compared with the example B, yt-

One of the solutions adopted to slow the sodium diftri m is replaced bythorium and magnesium. fusion is in locating the inner tube within anarea of an Yttrium may also be replaced by hafnium, aluminum outerenvelope filled with a neutral gas such as nitroand rare earth metalswithin limits from 0.1 mg to 5 mg. gen, at adequate pressure. Thus lampsare obtained in Although the addition of only one metal is sufficientwhich the electrode terminal voltage increases less rapit is clear thataddition of several metals of the above y with timementioned list mayalso be convenient.

TABLE 1 w B C Range of pressure and Exam- Exam- Exam- Materials weightsple Range ple Range ple Argon 10 to 40 torrs 20 10 to 40 tons. 20 10 to40 torrs- 20 Sodium iodide 10 to mg 25 10 to 50 mg 30 10 to 50 mg 30Tl1alliumi0didc 0.5 to 5 mg Indium iodide. 0.1 to 2.5 mg Cesium iodide0.5 to 5 mg 2. 5 Mercury iodide 0 to 10 mg. 10 Mercury 50 to 80 mg 75Yttrium 0.1 to 5 mg l Scandimn. 1 Thorium Magnesium SUMMARY or THElNVENTlON TABLE 2 It is therefore. an object of the present invention toD E R E E Materials Range x. ange x. provide an improved hlghpressuremercury vapor Argon mm 40mm 20 low 40 mm 20 electric discharge lampcontaining an alkali-metal halo- Sodium iodide 25 100 mg 50 40 w 80 mggcnidc, by including additional materials to maintain 6O Thqlliuflfliqdide 2 I05 s 3 thc o eratin v )lt' s b't' t' ll t t 'th t' lndmm md'demg 03 p g u 5 y cons an wl Cesium iodide 0.5 to 10 mg 5 0.5 to 10 mg 5In such lamps the alkali-metal halogenides, in particmercury iodide 5 tol0 mg g 5 to 20 mg lg ercury l8 l8 ular, may be sodiumhalogcnide and theadded materi- Yttrium OJ to 2 mg l 0 l to 2 mg 1 ails may includeadditions of mercury halogenlde, and Scandium 0.5 to 5 mg 2 a halogenideof easily ionizable metal and a further metal which may be in decreasingorder of preference: yttrium, thorium, magnesium, hafnium, aluminum andrare-earth metals.

Table 2 shows two examples of fillings for highpressure mercury-vaporlamps designed to provide a power of 1,000 watts, the burner diameterbeing 22 Table 3 shows two examples of fillings for highpressuremercury-vapor lamps designed for providing a power of 2,000 watts, theburner diameter being 30 mm and the spacing between electrodes of 145mm.

It has been observed that the high-pressure mercuryvapor lampsmanufactured according to the present invention have an operatingvoltage which is increased by less than two volts per thousand operationhours, which constitutes a substantial improvement with respect to priorart lamps of which the operation voltage was increasing by eight tofifteen volts per thousand operation hours.

While the present invention has been described in relation to specificembodiments, it is clear that the composition is not limited to theexamples and that other variations and modifications may be made withinthe scope of the invention as set forth in the appended claims.

What is claimed is:

l. A high-pressure mercury-vapor lamp filling comprising a mixture ofmaterials including mercury, sodium iodide, argon, mercury iodide,cesium iodide, yttrium and a further material selected from the groupconsisting of thallium iodide, indium iodide, scandium, thorium andmagnesium.

2. The lamp of claim 1 including an additional further material selectedfrom the group consisting of thallium iodide, indium iodide, scandium,thorium and magnesium.

2. The lamp of claim 1 including an additional further material selectedfrom the group consisting of thallium iodide, indium iodide, scandium,thorium and magnesium.